Lawyers acting for The X Factor judge Simon Cowell have warned UK newspapers not to harass their client after a tracking device was allegedly found attached to his Rolls Royce last week.

Law firm Carter-Ruck sent the warning letter to national newspapers on Friday after consulting with the presenter's publicist, Max Clifford, who told MediaGuardian.co.uk that "enough is enough".

According to Clifford, the letter pointed out that the use of a tracking device is illegal and could lead to prosecution.

He added that the identity of the journalist who allegedly attached the device is known to him and the individual concerned has been approached.

"We know who he is and we have marked his card and told him to never do anything like that again," Clifford said.

"We have always played the game and we are not precious but this is way beyond anything acceptable. So Carter-Ruck has sent a letter out to everybody warning them about this and making clear that it is unacceptable," he added.

"Simon has been putting up with this for seven years, with people approaching him at all hours and we know that we have got to have working relationships with the papers but within acceptable boundaries."

The letter also asked photographers and journalists not to pursue Cowell, place him under surveillance or photograph him in places where he has a reasonable expectation of privacy, including leaving or entering his home, Clifford said.

Asked if his client was upset about the alleged intrusion, Clifford added: "Simon is not getting stressed and not making a big drama about it but you know the game and he knows the game."

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